CD4~+T Cells Contributes To The Proliferation And Activation Of ILC2 In Lungs Of Mice During RSV Infection

Objective:Respiratory syncytial virus(RSV)is a major cause of bronchiolitis and pneumonitis in infants and young children.RSV also plays an important role in the formation and development of asthma.ILC2 can produce Th2 cytokines,such as interleukin-5(IL-5),interleukin-9(IL-9)and interleukin-13(IL-13),and is closely related to lung mucosal immunity.ILC2 may play an important role in RSV-induced eosinophilic infiltration and airway hyper-reactivity by producing IL-13 via the IL-33/ST2 pathway.ILC2 can increase the production of Th2-type cytokines in lungs,and augment the risk of the development of allergic asthma.As an important adaptive immune cell,CD4~+T cells have been shown to play a central role in the activation of immune cells and the induction of immune responses.It has been reported that papain induces ILC2 to secrete IL-9 dependent on CD4~+T cell-derived IL-2.In helminth infection,the survival of ILC2 requires the help of T cells,suggesting that T lymphocytes may act as a promoter on the biological activity of ILC2.Infection with RSV can induce an increase in the number and Th2 cytokines production of ILC2 in lung.However,whether the increased ILC2s are associated with CD4~+T cells?If CD4~+T cells are involved in the proliferation and activation of ILC2 during RSV infection is still unknown.Thus,in the present study,by using BALB/c mice that were infected intranasally with RSV,the function and mechanisms of CD4~+T cells in RSV-induced ILC2 proliferation and activation were investigated.Methods:Animal models with acute RSV infection have been established;Lung histopathology was determined by HE staining,the number of CD4~+T cells,IL-2~+CD4~+T cells,ILC2 and IL-5,IL-13 production of ILC2 in the lung determined by flow cytometry,adoptive transfer/block CD4~+T cells experiments were performed to identify the role of CD4~+T cells in RSV-induced airway inflammation,ILC2 were selected from lung and cultured for 24 hours to confirm the function of IL-2.Results:1.RSV infection enhances airway inflammation and pulmonary pathology.The total number of CD4~+T cells,IL-2~+CD4~+T cells,ILC2 and IL-5~+/13~+ILC2 in the lungs were increased significantly after infection,suggesting that both CD4~+T cells and ILC2were involved in RSV-induced airway inflammation.2.CD4~+T cells induce proliferation and activation of ILC2 during RSV infection.To further investigate the role of CD4~+T cells,CD4~+T cells were transferred into BALB/c mice before RSV infection.We found that adoptive transfer of CD4~+T cells elicited a massive infiltration of ILC2 in the lungs as compared with non-transferred mice.Blockade of CD4~+T cells with neutralizing anti-CD4 antibody can inhibit the number of ILC2 in the lungs of mice at 3 days after RSV infection.3.Expression of IL-2 in CD4~+T cells induces proliferation and activation of ILC2.To examine the role of IL-2,the expression of IL-2 mRNA in CD4~+T cells was evaluated.RSV infection significantly augmented the expression of IL-2 mRNA in CD4~+T cells.Adoptive transfer of CD4~+T cells resulted in an increase in the expression of IL-2 mRNA in the lung.However,treatment with anti-CD4 antibody diminished the level of IL-2 in the lung.ILC2 were isolated from the lungs of RSV-infected mice and re-stimulated in vitro with recombinant murine IL-2 for 24 h.The relative expression against?-actin of IL-5,IL-13 mRNA in pulmonary ILC2 was shown to be up-regulated by IL-2 stimulation.Conclusion:1.CD4~+T cells can enhance the proliferation and activation of ILC2 in RSV-infected mice.2.CD4~+T cells are major source of IL-2 during RSV infection.3.The proliferation and activation of ILC2 is IL-2 dependent manner.